OBJECTIVETo study the morphological characteristics and immunophenotype of highly cellular leiomyoma (HCL) of uterus, compared with that of uterine endometrial stromal tumors (EST).

METHODSHE and immuno-stained sections EnVision method from 20 cases of HCL, 21 cases of EST and 1 case of stromomyoma were reviewed. Monoclonal antibodies against h-caldesmon, calponin, CD10, desmin and smooth muscle actin (SMA) were used for immunohistochemistry studies.

RESULTSOn microscopic examination, HCL were densely cellular and composed of cells that ranged from spindle-shaped to round with scanty cytoplasm. A focal fascicular pattern was present in all cases. Blood vessels with large, thick muscular walls were a conspicuous feature of the majority of tumors. Cleft-like spaces were present in 9 tumors and 15 cases exhibited irregular focal extensions into the adjacent myometrium. ESTs were composed of cells that resembled endometrial stromal cells of proliferative endometrium. These cases included a significant component of delicate blood vessels similar to spiral arterioles. All 20 low grade endometrial stromal sarcoma cases had infiltrative growth to adjacent myometrium. Immunoreactivities of HCL for h-caldesmon, calponin, CD10, Desmin and SMA were 80.0% (16/20), 100% (20/20), 0 (0/20), 95.0% (19/20) and 100% (20/20), respectively, whereas the positive rates of EST were 4.7% (1/21), 23.8% (5/21), 66.7% (14/21), 23.8% (5/21) and 19.0% (4/21), respectively (P = 0.001).

CONCLUSIONSHighly cellular leiomyomas have distinct morphologic features. H-caldesmon, calponin, CD10, desmin and SMA are helpful in the differential diagnosis of HCL and EST.